1. Field of the Invention
The present invention relates to a sealed battery having a power generation which includes a positive electrode and a negative electrode and is housed in a battery case, and a battery pack provided with the sealed battery. In particular, the present invention relates to a sealed battery including an external positive terminal and an external negative electrode portion formed as a part of a battery case, and a battery pack provided with the sealed battery.
2. Description of Related Art
Heretofore, there have been known many sealed batteries each of which comprises a power generation element which includes a positive and negative electrodes and is housed in a battery case. For example, Japanese Unexamined Patent Publications (Kokai) Nos. 2001-93503 and 2001-93508 disclose such sealed batteries.
In the battery of Kokai No. 2001-93503, a plurality of negative electrodes and a plurality of positive electrodes are connected to current collecting plates, respectively. Each current collecting plate is provided with a connection projection which is fit in a connection hole perforated in a side wall of an electrolytic bath. Ends of the connection projections of adjoining unit cells are welded to each other to connect the unit cells in series. See FIGS. 2 and 7 and the corresponding explanation in Kokai No. 2001-93503.
In the battery of Kokai No. 2001-93508, a plurality of negative electrodes and a plurality of positive electrodes are connected to current collecting plates, respectively. A connection hole is perforated in a side wall of an electrolytic bath. A connection fitting is inserted in the connection hole. The current collecting plates of the adjoining unit cells are welded to each other through each fitting to connect the unit cells in series. See FIGS. 2 and 8 and the corresponding explanation in Kokai No. 2001-93508.
However, in the battery of Kokai No. 2001-93503 that the ends of the connection projections of the current collecting plates fitted in the connection holes of the electrolytic bath are welded to each other, a space has to be provided for a welding jig to be used for the welding. Therefore the connection hole would have to be formed in an upper portion of the electrolytic bath in order to avoid interference with the power generation element housed in the electrolytic bath. This inevitably results in an increased distance of an electrically conducting path from the positive and negative electrodes to a welded portion and further an increased electric resistance. In addition, the welding has to be performed from the inside of the electrolytic bath and hence the welding itself would not be easy.
In the battery of Kokai No. 2001-93508 that the current collecting plates are welded to the connection fittings inserted in the connection holes of the electrolytic bath, a space has to be provided for a welding jig to be used for the welding. Therefore the connection hole would have to be formed in an upper portion of the electrolytic bath in order to avoid interference with the power generation element housed in the electrolytic bath. Similarly, this inevitably results in an increased distance of an electrically conducting path from the positive and negative electrodes to a welded portion and further an increased electric resistance. In addition, the welding has to be performed from the inside of the electrolytic bath and hence the welding itself would not be easy.
As above, the conventional sealed batteries, which have to be designed to have a space therein for welding of the batteries, would be likely to include the long electrically conducting path from the power generation element to the external terminal of the battery and the large electric resistance. Further, the welding has to be performed from the inside of the electrolytic bath and hence the welding itself would not be easy.